@article{1250128110,
author = {Mawhin, J. and Ward, J.R.},
title = {Nonuniform nonresonance conditions at the two first eigenvalues for periodic solutions of forced Lienard and Duffing equations},
journal = {Rocky Mountain J. Math.},
volume = {12},
number = {4},
year = {1982},
pages = { 643-654},
language = {en},
url = {http://dml.mathdoc.fr/item/1250128110}
}
Mawhin, J.; Ward, J.R. Nonuniform nonresonance conditions at the two first eigenvalues for periodic solutions of forced Lienard and Duffing equations. Rocky Mountain J. Math., Tome 12 (1982) no. 4, pp. 643-654. http://gdmltest.u-ga.fr/item/1250128110/